How to erase the red dot marks altogether

Open the "Summary" tab (Summary tab will appear when pressing and holding the Monthly tab)

Tap the "Summary" tab once more (The dialog "Mark All as Read" will appear).

Tap "Mark All as Read".

※This will erase the red dot mark for all TimeTree calendars, with the exceptions of Notices, Feed tab, and public calendars. Please select and enter each pages and tabs to erase the red dot for those pages.